1. Field of the Invention
This invention relates generally to compressing color image data in a data processing system. Specifically, the present invention relates to a method for improving adaptive lossless data compression (ALDC) compression of color image data.
2. Description of Background
Currently, the ALDC compression algorithm is used in many data processing systems due to its data transmission speed and ability to handle any form of data. ALDC or LZ-1 is a compression algorithm that compresses the data by encoding repetitive strings of characters or bytes of data. Lossless compression algorithm means that no data is lost during the compression and decompression process. For example, when the ALDC compression algorithm is used in a printing device connected to a host computer via a communication link, for example, when ASCII, such as postscript files are sent to the printing device, the ALDC compression algorithm performs to maximize the performance of the communication link to the host computer. However, images embedded in documents to be printed may pose a problem in that raw image data (i.e., raw data bytes) typically has a high level of entropy and tends to compress in ALDC at a data expansion rate of up to approximately 12.5%. Thus, if the data has been encoded in one of many existing image compression algorithms, such as JPEG, JBIG, GIF or TIFF, for example, then the data has to be decompressed prior to transmission to the printing device. Further, the printing device is required to maintain input buffers at a level that will not interrupt printing.